Apparatus and method for thermal dissipation of photonic transceiving module

ABSTRACT

An apparatus for dissipating heat from a photonic transceiver module. The apparatus includes a top-plate member disposed in a length direction of a package for the photonic transceiver module. The apparatus further includes multiple fins formed on the top-plate member along the length direction from a backend position to a frontend position except at least one fin with a shorter length, forming an elongated void from the backend position to one backend of the at least one fin. Additionally, the apparatus includes a cover member disposed over the multiple fins with a horizontal sheet, two vertical side sheets, and a flange bent vertically from a middle portion of backend of the horizontal sheet. Furthermore, the apparatus includes a spring loaded in the elongated void between the flange and the one backend of the at least one fin to minimize an air gap at the backend of the horizontal sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority to U.S.patent application Ser. No. 16/578,090, filed Sep. 20, 2019, allcommonly assigned and hereby incorporated by references for allpurposes.

BACKGROUND OF THE INVENTION

The present disclosure is related to a photonics technology, moreparticularly, to an apparatus and a method for efficient thermaldissipation of a photonic transceiver module.

As science and technology are progressing rapidly, processing speed andcapacity of the computer increase correspondingly. The communicationtransmission or reception using the traditional cable is limited tobandwidth and transmission speed of the traditional cable, but the massinformation transmission required in modern life causes the traditionalcommunication transmission overload. To address such requirements, theoptical fiber transmission system replaces the traditional communicationtransmission system gradually. The optical fiber transmission systemdoes not have bandwidth limitation, and also has advantages ofhigh-speed data transmission, long transmission distance, its materialis impervious to electromagnetic waves. Therefore, the electronicsindustry performs research toward optical fiber transmission which willbecome the mainstream in the future. Said optical communication is atechnology in that light waves function as signal carriers andtransmitted between two nodes via the optical fiber. Field of opticalcommunication can be divided into optical communication side andelectric communication side according to transmission medium. By theoptical transceiver, the received optical signal can be converted to anelectrical signal capable of being processed by an IC, or the processedelectrical signal can be converted to the optical signal to betransmitted via optical fiber. Therefore, objective of communication canbe achieved.

The high-speed data transmission needs high-performance photonictransceiver which needs high efficiency heat dissipation during itsoperation. For example, a latest QSFP-DD transceiver module expects tomulti-fold of heat dissipation function over a module package size only20% bigger. Therefore, it is desired to have an improved apparatus forefficiently dissipating heat from a package of a photonic transceivermodule.

BRIEF SUMMARY OF THE INVENTION

The present disclosure is related to a photonics technology, moreparticularly, to an apparatus and a method for efficiently dissipatingheat away from a package of a photonic transceiver module. In certainembodiments, the invention is applied for high bandwidth opticalcommunication, though other applications are possible.

In modern electrical interconnect systems, high-speed serial links havereplaced parallel data buses, and serial link speed is rapidlyincreasing due to the evolution of CMOS technology. Internet bandwidthdoubles almost every two years following Moore's Law. But Moore's Law iscoming to an end in the next decade. Standard CMOS silicon transistorswill stop scaling around 5 nm. And the internet bandwidth increasing dueto process scaling will plateau. But Internet and mobile applicationscontinuously demand a huge amount of bandwidth for transferring photo,video, music, and other multimedia files. This disclosure describestechniques and methods to improve the communication bandwidth beyondMoore's law.

Serial link performance is limited by the channel electrical bandwidthand the electronic components. In order to resolve the inter-symbolinterference (ISI) problems caused by bandwidth limitations, we need tobring all electrical components as close as possible to reduce thedistance or channel length among them. Stacking chips into so-called 3-DICs promises a one-time boost in their capabilities, but it's veryexpensive. Another way to achieve this goal in this disclosure is to usemultiple chip module technology.

In an example, an alternative method to increase the bandwidth is tomove the optical devices close to electrical device. Silicon photonicsis an important technology for moving optics closer to silicon. In thispatent application, we will disclose a high-speed electrical opticsmultiple chip module device to achieve terabits per second speed, aswell as variations thereof Silicon photonics has led to development ofcompact packages of photonic transceiver modules in many pluggablespecifications. Yet, the compact package of powerful photonictransceiver module needs innovated design for efficiently dissipatingheat away during its operation.

In a specific embodiment, the present disclosure provides an apparatusfor dissipating heat from a photonic transceiver module. The apparatusincludes a top-plate member disposed in a length direction of a packagefor the photonic transceiver module. Additionally, the apparatusincludes multiple fins with one length formed on the top-plate memberalong the length direction from a backend position near middle of thetop-plate member to a frontend position except that an elongated void isformed from the backend position of the multiple fins to one backend ofat least one fin with a shorter length. Furthermore, the apparatusincludes a cover member disposed over the multiple fins with ahorizontal sheet, two vertical side sheets, and a flange bent verticallyfrom a middle portion of a backend of the horizontal sheet. Moreover,the apparatus includes a spring loaded in the elongated void between theflange and the one backend of the at least one fin for naturally pushingthe cover member to slide backward beyond the backend position of themultiple fins until the backend of the horizontal sheet is stoppedagainst an object.

In another aspect; the present disclosure provides a method ofdissipating heat from a package of a photonic transceiver module. Themethod includes a step of setting a top-plate member disposed in alength direction of the package. Additionally, the method includesforming multiple fins of one length on the top-plate member along thelength direction from a backend position near middle of the top-platemember to a frontend position except an elongated void being formed fromthe backend position of the multiple fins to one backend of at least onefin with a shorter length. Furthermore, the method includes disposing acover member over the multiple fins with a horizontal sheet, twovertical side sheets, and a flange bent vertically from a middle portionof a backend of the horizontal sheet. Moreover, the method includesloading a spring in the elongated void between the flange and the onebackend of the at least one fin for naturally pushing the cover memberbackward beyond the backend position of the multiple fins until thebackend of the horizontal sheet is stopped against an object.

In yet another aspect, the present disclosure provides a packagestructure for a photonic transceiver module comprising an apparatus ofclaim 1 for dissipating heat up to 20 W therefrom.

The present invention achieves these benefits and others in the contextof known technology. However, a further understanding of the nature andadvantages of the present invention may be realized by reference to thelatter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this process andscope of the appended claims.

FIG. 1 is a side view of a photonic transceiver module with externalheat sink plugged into a custom system equipment according to anembodiment of the present invention.

FIG. 2 shows both a top view and a side view of an external heat sinkphotonic transceiver package structure with lid according to theembodiment of the present invention.

FIG. 3 is a perspective exploded view of an external heat sink formed ona package of a photonic transceiver module according to an embodiment ofthe present invention.

FIG. 4A is a perspective top view of a cover member of the external heatsink of FIG. 3 according to the embodiment of the present invention.

FIG. 4B is a perspective bottom view of the cover member and a loadedspring of the external heat sink of FIG. 3 according to the embodimentof the present invention.

FIG. 5 is a perspective view of a photonic transceiver module having afixed external heat sink plugged into a custom system having an internalthermal dissipation equipment according to an embodiment of the presentinvention.

FIG. 6A is a side view of the external heat sink of FIG. 5 with a covermember being at a position separated by an air gap from a face plate ofthe internal thermal dissipation equipment according to the embodimentof the present invention.

FIG. 6B is a side view of the external heat sink of FIG. 5 with a covermember being at a position with a minimized air gap from the face plateof the internal thermal dissipation equipment according to theembodiment of the present invention.

FIG. 6C is a cross-section view of the external heat sink of FIG. 6Bwith a cover member being pushed by the loaded spring to the positionwith the minimized air gap from the face plate of the internal thermaldissipation equipment according to the embodiment of the presentinvention.

FIG. 7 is a flow chart illustrating a method of thermal dissipation fora package of a photonic transceiver module according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure is related to a photonics technology, moreparticularly, to an apparatus and a method for efficiently dissipatingheat away from a package of a photonic transceiver module. In certainembodiments, the invention is applied for high bandwidth opticalcommunication, though other applications are possible.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,horizontal, vertical, side, inner face, outer face, forward, reverse,clockwise and counter-clockwise have been used for convenience purposesonly and are not intended to imply any particular fixed direction.Instead, they are used to reflect relative locations and/or directionsbetween various portions of an object.

FIG. 1 is a side view of a photonic transceiver module with externalheat sink plugged into a custom system equipment according to anembodiment of the present invention. The photonic transceiver module hasbeen developed very fast in resent years to provide high data rates of4×10 Gbit/s, 4×28 Gbit/s or higher for high-speed data communicationsapplications. The photonic transceiver module is also characterized byits small form factor pluggable package structure. For example, Asshown, the package structure is compatible with the Quad SmallForm-factor Pluggable (QSFP) specification, or Quad Small Form-factorPluggable Double-Density (QSFP-DD) specification, or latest Quad SmallForm-factor Pluggable Double-Density Type II (QSFP-DD Type 2)specification. With high data rate being provided, higher laser powerand higher frequency may be involved, yielding more heat during itsoperation. Thermal dissipation of the heat generated by the photonicstransceiver modules has become a key focus for new module mechanicaldesign. Past designs only had to dissipate 2-4 W of power, but thestate-of-art modules are expected to dissipate up to 20 W in a packagethat is only 25% larger in size than past design.

Referring to FIG. 1, using the QSFP-DD module as an example, the package100 (of the photonics transceiver module) usually is coupled with aninternally air-cooled thermal sink 300 associated with customer networksystem frame for heat dissipation. Because of the higher thermal load ofnewer modules in the QSFP-DD specification, an external thermal sink 200fixed to a top-plate member of the package 100 has been proposed foradded cooling efficiency. The external thermal sink 200 is integrated onthe top-plate member along a length direction from a first position at afrontend of the package 100 to a second position near middle region ofthe top-plate member. The external thermal sink 200 has a fixed coverover multiple fins, all having a length of L, to form multiple air-flowchannels in gaps between neighboring fins under the cover. As thephotonics transceiver module is plugged to the network system frame, thesecond position of the external heat sink 200 must be set just outside abezel face plate 301 of the internally air-cooled thermal sink 300. Thebezel face plate 301 has been configured to have multiple through-holes.As air is pulled by a fan from the internally air-cooled thermal sink300 inside a customer system frame, air is assumed to be pulled throughthe air-flow channels in the integrated external thermal sink 200 tohelp dissipate heat on the front of the photonics transceiver module.

FIG. 2 shows both a top view and a side view of an external heat sinkphotonic transceiver package structure with lid according to theembodiment of the present invention. Referring to FIG. 1 and FIG. 2, thesecond position of the external heat sink is a backend position of thecover as well as the multiple fins of the length L. Due to mechanicaltolerancing of the face plate 301 of the internally air-cooled thermalsink 300 on its thickness and position relative to system frame, thebackend position of the cover of the external heat sink 200 must belimited with a nominal gap G of about 1 (or 2) mm from the customerbezel face plate 301. Because of this gap, pulling air over the multiplefins of the external heat sink 200 is like having a hole in a straw,where the air flow will be greatly reduced to impact thermaldissipation.

In some implementations, referring to FIG. 1, the face plate design ofthe customer system frame includes an EMI finger 302 disposed inbetween. In such a configuration, a first photonics transceiver modulepackage 100A is plugged in at a higher position with a first externalheat sink 200A facing a face plate 301 and a second photonicstransceiver module package 100B is plugged at a lower position with asecond external heat sink 200B facing an end face of EMI finger 302.Again, the mechanical tolerance requires a first gap G to be existedbetween the backend of the first external heat sink 200A and the faceplate 301 and a second gap G′ between the backend of the second externalheat sink 200B and the end face of the EMI finger 302. For bothplugged-in packages 200A and 200B of the photonics transceiver modules,the gap G and G′ make the air-flow channels less ideal in respective twosituations.

FIG. 3 is a perspective exploded view of an external heat sink formed ona package of a photonic transceiver module according to an embodiment ofthe present invention. Referring to FIG. 3, the external heat sink isconfigured with multiple fins 201 formed vertically on the top-platemember 101 of the package 100 of the photonics transceiver module. Inthe embodiment, the external heat sink with the multiple fins is formedin region near front end 111 of the package 100. Optionally, a backendregion of the package 100 includes electrical connector pins pf thephotonics transceiver module for connecting with network systemequipment on the other side of the face plate 301 of custom system frame(see FIG. 1). Optionally, the fins are equally separated by a gapdistance. All except at least one (203) of the multiple fins 201 haveone height above the top-plate member 101 and one length from a firstposition (front end 202 a) to a second position (backend 202 b). The atleast one fin is shorter in length with its backend 207 b in a retractedposition relative to the backend 202 b of all rest fins 201, forming anelongated void 203 c from the backend 202 b of all rest fins 201 to the203 b of the at least one fin 203 with a width of two gap distances.Additionally, the multiple fins 201 include two out-most fins with afirst fin 204 fixed at a first edge position (fully visible in FIG. 3)and a last fin 205 fixed at a last edge position (partially visible inFIG. 3). Each of these out-most fins is configured with two notches,e.g., 206 a and 206 b, on the outer face of the first fin 204. Thenotches on the outer face of the last fin 205 is not directly visible inFIG. 3.

FIG. 4A is a perspective top view of a cover member of the external heatsink of FIG. 3 according to the embodiment of the present invention.FIG. 4B is a perspective bottom view of the cover member and a loadedspring of the external heat sink of FIG. 3 according to the embodimentof the present invention. Referring to FIG. 4A, FIG. 4B, as well as FIG.3 shown before, the external heat sink includes a cover member 210configured to cover the entire multiple fins 201 and a spring 220configured to be loaded under the cover member 210 into the elongatedvoid 203 c. The cover member 210 further is characterized by arectangular shaped horizontal sheet 211 with a front end 212 a and abackend 212 b along its length direction, two vertical side sheets 214and 215 connected (along downward direction) to two length edges of thehorizontal sheet 211. Each of the two vertical side sheets is configuredwith two slots e.g., 216 a and 216 b for side sheet 214, positioned tofit with the two notches, e.g., 206 a and 206 b, on the correspondingfirst out-most fin 204 (or the last out-most fin 205) for at leastpartially lock the cover member 210 substantially entirely over themultiple fins. Each slot 216 a or 216 b is made with extra free lengthof a few mini-meters to allow the cover member 210 to be laterallymoveable along the length direction while being partially locked withfins (particularly two out-most fins 204 and 205) by the notches inslots. Furthermore, the cover member 210 also includes a vertical flange213 being set to bent from a middle part of the backend 215 of the covermember 210. Optionally, the vertically flange is positionedcorresponding to the elongated void 203 c. In the embodiment, the spring220 is loaded in the elongated void 203 c and stopped between thevertical flange 213 and the backend 207 b of the at least one fin 203 inshorter length as the cover member 210 is disposed to cover the multiplefins 201. The spring 211 naturally push the cover member 210 backward asit is slide up to the extra free space provided with the two slots (216a and 216 b) of each (e.g., 214) of two vertical side sheetsrespectively with two notches (206 a and 206 b) being locked therein.

In addition to the exploded view of the package 100 of the photonicstransceiver module with a fixed external heat sink 200 (cover member210, spring 220, and multiple fins 201 fixed to the package 100), FIG. 5shows a photonic transceiver module having the fixed external heat sinkbeing plugged into an internal thermal dissipation equipment of a customsystem frame according to an embodiment of the present invention.Referring to FIG. 5, the internal thermal dissipation equipment 400 isconfigured with an air-cooled heat sink coupled to an electric-power fan420 at its backend and a face plate 410 with multiple through-holes atits front end. The fan 420 draws an air flow through air-flow channelsformed between gaps between the multiple fins under the cover member todissipate heat from the front end of the photonics transceiver moduleinto the internal thermal dissipation equipment 400. As the photonicstransceiver module is plugged in with its backend being inserted fullyinside the internal thermal dissipation equipment 400, the backend ofthe external heat sink 200 is designed to be left outside butsubstantially close to the face plate 411 except a nominal gap for roomof mechanical tolerance of the internal thermal dissipation equipment400. Typically, this nominal gap is limited to about 1 millimeter. Asdescribed earlier in FIG. 3, FIG. 4A, and FIG. 4B, the cover member(210) is designed to be pushed by the loaded spring 220 to slide alongthe length direction relative to the fixed fins (201, 204, 203, 205),provided with the extra free distance of the slot (e.g., 216 a) relativeto the size of the notch (e.g., 206 a). When the extra free distance isset to be at least larger than the nominal gap, the backend (211) of thecover member 210 is naturally pushed by the loaded spring 220 to touchthe face plate 411, thus closing or at least minimizing the gap.Optionally, the nominal gap is about 1 millimeter and the extra freedistance of the slot versus the notch can be set to be 2 or moremillimeters.

FIG. 6A is a side view of the external heat sink of FIG. 5 with a covermember being at a position separated by an air gap from a face plate ofthe internal thermal dissipation equipment according to the embodimentof the present invention. Referring to FIG. 6A, this is a plugged-inconfiguration of the package 100 of photonics transceiver module with afixed external heat sink 200. This configuration is substantially sameas related art where there is an air gap G>0 from the backend of thecover member 210 of the external heat sink 200 to a face plate 410 ofthe internal thermal dissipation equipment 400. This gap G isintentionally left by design due to manufacture tolerance of theinternal thermal dissipation equipment 400. As seen, the cover member210 is disposed with the two notches 206 a and 206 b fit in thecorresponding two slots 216 a and 216 b on the outer face of theout-most fin (204). The package 100 is in a plugged-in position inassociation with the internal thermal dissipation equipment 400. The airgap G>0 causes reduced efficiency in thermal dissipation of the externalheat sink 200.

FIG. 6B is a side view of the external heat sink of FIG. 5 with a covermember being at a position with minimized air gap from the face plate ofthe internal thermal dissipation equipment according to the embodimentof the present invention. Referring to FIG. 6B, this is substantiallythe same plugged-in position associated with the external heat sink 200versus the face plate 410 of the internal thermal dissipation equipment400 but with an air gap G˜0. The backend (212 b) of the cover member 210slides as indicated to touch the face plate 410, making the air gap Gminimized to reduce loss of air flow and improve thermal dissipationefficiency. FIG. 6C shows a cross-section view of the external heat sinkof FIG. 6B. This clearly illustrates the function of the loaded spring210 under the a cover member (stopped between the vertical flange (213)and the backend (207 b) of the at least one fin (203) for naturallypushing the backend (212 b) of the cover member 210 to be against theface plate 410 to minimize the air gap G (˜0).

As shown in FIG. 6B and FIG. 6C in the side views, the horizontal sheetof the cover member (211) is disposed on top ridges of multiple fins andhas a same leveled backend with vertical side sheets. The cover memberand the multiple fins together form multiple air flow channels in thegaps between neighboring fins to become effective external heat sink forpulling heat of the package through the air flow channels into theinternal thermal dissipation equipment. As the backend of the covermember, for both horizontal sheet and two vertical sheets, touches theface plate of the internal thermal dissipation equipment, the nominalgap there left due to mechanical tolerance can be closed or at leastminimized. The minimized air gap between the backend of the cover memberand the face plate of the internal thermal dissipation equipmentsubstantially enhance heat dissipation efficiency. Optionally, theexternal heat sink as formed in the embodiment described herein caneffectively dissipate heat over 20 W from the front end region of thephotonics transceiver module.

In another aspect, the present disclosure provides a package for acompact photonics transceiver module. The package includes an externalheat sink described herein to pull air flow therefrom for dissipatingheat up to 20 W out of the front region of the photonics transceivermodule. The package is a compact and pluggable type configured to inQuad Small Form-Factor Pluggable (QSFP) specification. Alternatively,the package is a compact and pluggable type configured to in Quad SmallForm-Factor Pluggable Double Density (QSFP-DD) specification.Optionally, the package is a compact and pluggable type configured to inQuad Small Form-Factor Pluggable Double Density Type II (QSFP-DD type 2)specification.

In yet another aspect, the present disclosure provides a method ofdissipating heat out of a package of a photonic transceiver module,especially for high-power photonics transceiver module in compact formfactor for high-speed data communication. FIG. 7 shows a flow chartillustrating a method of thermal dissipation for a package of a photonictransceiver module according to an embodiment of the present invention.Referring to FIG. 7 and further referring to FIG. 3, FIG. 6B and FIG.6C, the method is implemented through an apparatus described herein fordissipating heat up to 20 W out of front region of the package ofphotonics transceiver module. In the embodiment, the method includes astep of setting a top-plate member disposed in a length direction.Particularly, the method employs an apparatus for dissipating heat outof the package (such as one in QSFP-DD specification) of the photonicstransceiver module.

Additionally, the method includes a step of forming multiple fins of onelength on the top-plate member along the length direction from a backendposition near middle of the top-plate member to a frontend positionexcept an elongated void being formed from the backend position of themultiple fins to one backend of at least one fin with a shorter length.The multiple fins fixed vertically on the top-plate member to becomeparts of an external heat sink located near front end region of thepackage. Optionally, all fins including the at least one fin with theshorter length has a same height and equal separation (gap) from itsneighboring fins. Optionally, all fins including the at least one finwith the shorter length have a leveled front end at a first position onthe top-plate member near the front end of the package. Optionally, allfins except the at least one fin with the shorter length have a leveledbackend at a second position near middle region of the package.Optionally, each of the two out-most fins (the first fin and the lastfin) has two notches formed on its outer face separated with a spacingin the length direction.

Furthermore, the method includes a step of disposing a cover member overthe multiple fins with a horizontal sheet, two vertical side sheets, anda flange bent vertically from a middle portion of a backend of thehorizontal sheet. In the embodiment the cover member described here isanother part of the external heat sink. Optionally, the horizontal sheetof the cover member is a rectangular shape having a length at leastlonger than the length of the fins. Optionally, the two vertical sidesheets are bent from two opposed side edges of the horizontal sheet andhave a same length as that of the horizontal sheet and a same (orlarger) height as (than) the height of the fins. Each of the twovertical side sheets is configured to have two slots formed inrespective position for the two notches on the outer face of theout-most fin to fit in while with extra free spacing in the lengthdirection. Optionally, the flange is substantially aligned with theelongated void to face the backend of the at least one fin with theshorter length. As the cover member is disposed in position, thehorizontal sheet is in touch with top ridges of all fins and the slotson the two vertical side sheets take the notches to partially lock thecover member with the fins. Optionally, the flange is substantiallyaligned with the elongated void to face the backend of the at least onefin with the shorter length as the cover member is disposed in theposition described above.

Moreover, the method including loading a spring into the elongated voidwhile disposing the cover member into the position over the multiplefins and having the notches partially being locked by the slots. Theloaded spring is stopped between the flange and the backend of the atleast one fin with the shorter length. Naturally, the loaded springpushes the cover member to be movable laterally along the lengthdirection allowed by the extra free spacing set for the slots. Thebackend of the cover member is able to slide backward. Provided that theextra free spacing is larger than a designed nominal gap of about 1 mmto a system frame in which the package of the photonics transceivermodule is plugged, the backend of the cover member is naturally in touchwith a face plate of the system frame (in some embodiments, it is aninternal thermal dissipation equipment associated with a custom networksystem). In other words, the step of the method naturally close or atleast minimize an air gap caused by the designed nominal gap thatresults in leak of air flow in the multiple air flow channels of theexternal heat sink. As the result, the heat dissipation efficiency ofthe external heat sink is substantially enhanced. Optionally, the methodis have the external heat sink described above to effectively dissipateheat up to 20 W away from the front end region of the photonicstransceiver module.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. An apparatus for dissipating heat, from aphotonic module, the apparatus comprising: a top-plate member disposedin a length direction of a package for the photonic module; a pluralityof fins with one length formed on the top-plate member along the lengthdirection of the package for the photonic module from a backend positionof the plurality of fins near a middle of the top-plate member to afrontend position, an elongated void being formed from the backendposition of the plurality of fins to a backend of at least one fin ofthe plurality of fins with a shorter length; a cover member disposedover the plurality of tins with a horizontal sheet, two vertical sidesheets, and a flange bent vertically from a middle portion of a backendof the horizontal sheet; and a spring loaded in the elongated voidbetween the flange and the one-backend of the at least one fin of theplurality of fins for pushing the cover member to slide backward beyondthe backend position of the plurality of fins until the backend of thehorizontal sheet is stopped against an internal thermal dissipationequipment.
 2. The apparatus of claim 1 wherein the plurality of fins,the cover member, and the spring define an external heat sink that, iscoupled to a face plate of the internal thermal dissipation equipment.3. The apparatus of claim 2 wherein the plurality of fins is configuredvertically on the top-plate member with a same height and a gap betweenany two neighboring ones of the plurality of fins throughout the onelength of the plurality of fins with the backend position of theplurality of fins being separated by a gap distance of about 1 to 2millimeters from the face plate of the internal thermal dissipationequipment as the photonic module is plugged in.
 4. The apparatus ofclaim 3 wherein the plurality of fins comprises two outermost fins, eachof the two outermost fins having two notches formed at an outer facethereof.
 5. The apparatus of claim 4 wherein each of the two verticalside sheets of the cover member comprises two slots respectively forfitting the two notches so that the cover member is partially lockedwith the plurality of fins, each of the two slots having extra freespacing relative to the two notches larger than the gap distance in thelength direction of the package for the photonic module.
 6. Theapparatus of claim 5 wherein the extra free spacing is configured to belarger than the gap distance for the cover member to move laterallyalong the length direction of the package for the photonic module as thespring pushes the backend of the horizontal sheet against the face plateof the internal thermal dissipation equipment.
 7. The apparatus of claim5 wherein the horizontal sheet, of the cover member is disposed to touchtop ridges of the plurality of fins to form a plurality of air flowchannels in gaps between two neighboring ones of the plurality of finsfor pulling heat of the package for the photonic module into theinternal thermal dissipation equipment to minimize an air gap betweenthe backend of the horizontal sheet and the face plate of the internalthermal dissipation equipment.
 8. The apparatus of claim 1 wherein thepackage for the photonic module comprises an optical transceiver modulein Quad Small Form-Factor Pluggable (QSFP) specification.
 9. Theapparatus of claim 1 wherein the package for the photonic modulecomprises an optical transceiver module in Quad Small Form-FactorPluggable Double Density (QSFP-DD) specification.
 10. The apparatus ofclaim 1 wherein the package for the photonic module comprises an opticaltransceiver module in Quad Small Form-Factor Pluggable Double DensityType II (QSFP-DD type 2) specification.
 11. A package structurecomprising the apparatus of claim 1 for dissipating heat up to 20 Wtherefrom.
 12. The package structure of claim 11 wherein the photonicmodule is configured to be an optical transceiver module in Quad SmallForm-Factor Pluggable Double Density Type 11 (QSFP-DD type 2)specification.
 13. A method of dissipating heat from a package for aphotonic module, the method comprising: setting a top-plate memberdisposed in a length direction of the package for photonic module;forming a plurality of fins of one length on the top-plate member alongthe length direction of the package for the photonic module from abackend position of the plurality of fins near a middle of the top-platemember to a frontend position, an elongated void being formed from thebackend position of the plurality of fins to a backend of at least onefin of the plurality of fins with a shorter length; disposing a coverover the plurality of fins with a horizontal sheet, two vertical sidesheets, and a flange bent vertically from a middle portion of a backendof the horizontal sheet; and loading a spring in the elongated voidbetween the flange and the backend of the at least, one fin of theplurality of fins for pushing the cover member backward beyond thebackend position of the plurality of fins until the backend of thehorizontal sheet is stopped against an internal thermal dissipationequipment.
 14. The method of claim 13 wherein providing the plurality offins, the cover member, and the spring forms an external heat sinkcoupled to a face plate of the internal thermal dissipation equipmentfor the photonic module.
 15. The method of claim 14 wherein forming theplurality of fins comprises configuring each fin vertically with aheight on the top-plate member and laterally with a gap between any twoneighboring fins throughout the one length of the plurality of fins withthe backend position of the plurality of fins being separated by a gapdistance of about 1 to 2 millimeters from the face plate of the internalthermal dissipation equipment as the photonic module is plugged in. 16.The method of claim 15 wherein forming the plurality of fins comprisesforming two notches at each outer surface of two of the plurality oftins located at two outermost locations among the plurality of fins. 17.The method of claim 16 wherein disposing the cover member compriseshaving two slots formed at the two vertical side sheets to fit with thetwo notches for partially locking the cover member with the plurality offins, each of the two slots having extra free spacing relative to thetwo notches larger than the gap distance in the length direction of thepackage for the photonic module.
 18. The method of claim 17 wherein theextra free spacing is configured to be larger than the gap distance forthe cover member to be moveable laterally along the length direction ofthe package as the spring pushes the backend of the horizontal sheetagainst the face plate of the internal thermal dissipation equipment.19. The method of claim 15 wherein disposing the cover member furthercomprises forming a plurality of air flow channels for pulling heat ofthe package through the plurality of fins into the internal thermaldissipation equipment to minimize an air gap between the backend of thehorizontal sheet and the face plate of the internal thermal dissipationequipment.
 20. The method of claim 19 wherein forming the plurality ofair flow channels to minimize the air gap between the backend of thehorizontal sheet and the face plate of the internal thermal dissipationequipment further comprises providing thermal dissipation up to 20 W inheat power.